In addition to the basic vehicle window wiper functions of OFF, MIST (single wipe), LOW speed, and HIGH speed, it is now common to provide an AUTO-DELAY function wherein a delay time of the wipers is automatically controlled in accordance with a water drop sensor which senses the presence of water drops on a vehicle window, such as a windshield. An exemplary water drop sensor comprising a pair of electrodes disposed in association with a portion of a surface of a vehicle window within a wipe pattern is disclosed in U.S. Pat. No. 5,304,936, which patent is assigned to the assignee of the present invention.
Typically, an electronic control circuit, and more particularly an auto-delay controller controls a wiper drive motor in accordance with an output of the water drop sensor when the AUTO-DELAY function is selected. The auto-delay controller executes an auto-delay algorithm or control program to control the wiper drive motor in accordance with the water drop sensor output. The control program outputs control information to a wiper motor controller, and inputs wiper blade position information for use in controlling the wiper drive motor. Wiper position information is generated by a switching device mechanically coupled to the wiper drive motor which indicates when the wipers are in a predetermined position, for instance, an inner wipe position wherein the wiper blades are situated at the bottom of a windshield. The inner wipe position information is used as feedback to insure proper wiper blade operation and is typically routed from the switching device to the auto-delay controller through the wiper motor controller.
One arrangement for interfacing the wiper motor controller to the auto-delay controller is to provide separate input and output data lines therebetween. However, there are incremental cost and design disadvantages associated with providing separate data lines. There is also reduced circuit reliability associated with using multiple data lines.
What is needed therefore is a low cost, highly reliable arrangement for interfacing a window wiper control switch, a wiper motor controller, and an auto-delay controller to permit a water drop sensor to control a window wiper delay time period.